The advantages of controlled release products are well known in the pharmaceutical field and include the ability to maintain a desired blood level of a medicament over a comparatively longer period of time while increasing patient compliance by reducing the number administrations. These advantages have been attained by a wide variety of methods. For example, different hydrogels have been described for use in controlled release medicines, some of which are synthetic, but most of which are semi-synthetic or of natural origin. A few contain both synthetic and non-synthetic material. However, some of the systems require special process and production equipment, and in addition some of these systems are susceptible to variable drug release.
Oral controlled release delivery systems should ideally be adaptable so that release rates and profiles can be matched to physiological and chronotherapeutic requirements. In U.S. Pat. Nos. 4,994,276, 5,128,143, and 5,135,757, hereby incorporated by reference in their entireties, it is reported that a controlled release excipient which is comprised of a synergistic combination of heterodisperse polysaccharides (e.g., a heteropolysaccharide such as xanthan gum in combination with a polysaccharide gum capable of cross-linking with the heteropolysaccharide, such as locust bean gum, in an aqueous environment) is capable of being processed into oral solid dosage forms using either direct compression (i.e., dry granulation), following addition of drug and lubricant powder, conventional wet granulation, or a combination of the two. The release of the medicament from the formulations therein proceeded according to zero-order or first-order mechanisms.
The controlled release excipients disclosed in U.S. Pat. Nos. 4,994,276, 5,128,143, and 5,135,757 are commercially available under the trade name TIMERx.RTM. from Edward Mendell Co., Inc., Patterson, N.Y., which is the assignee of the present invention.
European Pat. No. 234670 B describes a controlled-release pharmaceutical formulation containing xanthan gum wherein the xanthan gum comprises from about 7.5 to about 28 percent, by weight, of the formulation except for a formulation wherein the controlled release carrier comprises a mixture of 15-50 parts by weight dimethylsiloxane, 30-100 parts by weight silicic acid, 30-100 parts by weight mannans or galactans or a mixture thereof, 50-150 parts by weight xanthans and 5-75 parts by weight micronized seaweed.
However, heretofore there has been no teaching of a controlled release formulation providing a novel and unexpected combination of suitable proportions of a homopolysaccharide such as, e.g., xanthan gum, a heteropolysaccharide, such as, e.g., locust bean gum, together with an inert diluent and a pharmacologically acceptable hydrophobic material, so as to provide an improvement in controlled release properties for such an active medicament.